class_docstr: Mutate the leaf node (i.e., ValueChoice) of parameter choices.
  
  Should be used together with :class:`ParameterChoiceMutator`.
code: def mutate(self, model: GraphModelSpace) -> None:
      # NOTE: leave a record here
      # real mutations will be done in ParameterChoiceMutator
      self.choice(self.candidates)
  
imports: from __future__ import annotations
  from typing import Any, List, Tuple, Dict, Iterable, cast
  from nni.mutable import MutableExpression, Categorical, frozen_context, label_scope
  from nni.nas.space import Graph, GraphModelSpace, Node, StationaryMutator, Mutator
  from nni.nas.space.graph_op import Cell
label_desc: Use image node_id 2 for calling the ParameterChoiceLeafMutator obj's underlying member method code with example usage: obj.mutate(model) without return types